Ferroelectric materials contain permanent electric dipoles which can be aligned in order to store a permanent electric polarization within the material. Devices made with ferroelectric materials can be used as memory elements, transducers, and resonators. It is desirable to make devices smaller, for instance by utilizing thin films. However, ferroelectricity in thin films is affected by size. It was thought that there was a critical size below which stable ferroelectric behavior could not be maintained in thin films. For example, researchers have found that BaTiO3 films with SrRuO3 electrodes do not possess ferroelectricity where the ferroelectric film is less than 24 Angstroms thick, and further state that ferroelectricity will be suppressed relative to bulk for films between 24 and 150 Angstroms thick (J. Junquera and P. Ghosez, Nature (London) 422, 506 (2003)). As a result, devices using thin films were thought to have a lower size limit, below which useful ferroelectric structures could not be made. This lower limit on the size of useful ferroelectric structures creates a limit on the size of devices and systems incorporating such structures, such as data storage systems. Accordingly, it is desirable to be able to overcome this perceived lower limit to create even thinner ferroelectric structures.
An additional consideration is that ferroelectric thin films are known to experience fatigue, meaning that after some number of switching cycles the polarization of the film can no longer be switched. Therefore, while it is desirable to be able to overcome the perceived lower thickness limit of useful ferroelectric structures, it is also desirable to inhibit fatigue in such structures and to provide high polarization.